ELECTRICAL HARNESSING ARTICLE

Abstract: A highly-expanded heat-recoverable article intended primarily for automative electrical harnessing has unusually high expansion ratios (e.g. greater than 4:1) and preferably in a relatively flat tubular shape of high aspect ratio (e.g. 6:1). Preferred convolutions for flexibility are prevented from splitting by means of controlled radii of curvature of the corners of the convolutions and by the use (unusual in heat-recoverable materials) of reinforcing fillers, which also permit relatively high levels of cross-linking to avoid "amnesia" on recovery.

Description: ELECTRICAL HARNESSING ARTICLE This invention relates to a dimensionally heat-recoverable article for harnessing electrical -wires and cables. The invention is especially suitable for bulkhead cable feed- throughs in commercial automotive manufacturing, where existing rubber feed-throughs are unsatisfactory. One such known feed- through is shown by way of explanation in the accompanying schematic Sketch A, wherein the rubber article B having a convoluted mid-section B' for flexibility, has been snap-fitted into an aperature of bulkhead C (shown in section) and is held therein by its lip-and- groove grommet end formation D. The other end E of the feed- through B tapers to grip cable F comprising a number of wires G which pass through the feed-through B and are connected to various plugs or other electrical components H. Similar plugs or components may be attached at the other ends (not shown) of the wires G to connect the various automotive electrical circuits, which are nowadays becoming increasingly complex. These known rubber feed- throughs must be fitted over the cable before the plugs etc. are attached, and this reduces the efficiency of the harnessing process, especially as the tapered end E of the feed-through must be resiliently stretched in order to fit over and grip the cable. Moreover, the softness and resilience of the rubber makes it undesirably easy to dislodge the snap-fit grommet end from the bulkhead C, or to push the grommet end right through the aperature in the bulkhead C, thereby losing the necessary sound-proofing and sealing effects of the feed-through. One aspect of the present invention provides a highly advantageous feed-through in the form of a hollow dimensionally heat-recoverable article of high expansion ratio, by which is meant that the average inner diameter of at least part of the expanded ready- to-apply article is at least four times (preferably at least five times, more preferably at least six times) the average inner diameter of the same part(s) of the article in its unexpanded state, and that preferably all parts of the expanded article have an average inner diameter at least 1.5 times (preferably at least 1.8 times, more preferably at least 2.0 times) that of the same parts of the article in its unexpanded state. Such articles are hereinafter referred to as "high-expansion" or "highly-expanded" articles, having expansion ratios of at least 4: 1, 5: 1, 6:1 , 1.5: 1 , 1.8: 1 , and 2: 1 respectively. Preferably the feed-through articles are expanded to form a substantially straight tube of substantially constant tubular cross-section. The average diameter is that of a notionally circular article and may be measured with the article held in an approximately circular configuration or may be calculated from the measured circumference divided by Pi. A great advantage of the high-expansion feed-through articles according to one aspect of this invention is that they can conveniently be slid onto the cable after the relatively bulky plugs etc. have been connected to the wires and can thereafter still be heat-recovered to grip the relatively slim cable. This can be achieved with a "normal" round tubular shape, but a much preferred form of the invention provides the highly-expanded articles with a relatively flat tubular shape having a tubular aspect ratio (longest internal "diameter" to shortest internal "diameter" looking along the tubular axis) of at least 3:1, preferably at least 4:1, more preferably at least 5:1, and especially at least 6: 1. Preferably, the tube will not be severely flattened to a substantially closed state, which means that the aspect ratio is preferably less than 25: 1, more preferably less than 15: 1, especially less than 10: 1. This relatively flat shape has the advantage that, while the plugs etc. attached to the cable wires can easily pass through the highly-expanded article, with flexing of its side walls if necessary, the flattened shape can be of dimensions pre-selected to grip gently on the cable wire bundle, thus holding the article conveniently in position prior to heat recovery, and presenting a uniform aspect of cable and feed -through for efficient heating from opposite sides of its main flattened surfaces. This aspect of the invention is illustrated by way of example in Figure 1 of the accompanying drawings, which shows schematically the highly-expanded feed-through 1 having a relatively flat shape of aspect ratio L:S about 7: 1 gently gripping the cable wire bundle 2. Heaters 3 are shown schematically directing heat toward the virtually identical upper and lower aspects of the assembly. This has the effect of recovering the article 1 relatively uniformly about the cable 2, thus avoiding displacement which could result from distortion caused by uneven recovery. Such distortion and displacement can be a problem with articles having the aforementioned "normal" round shape, since these will hang asymmetrically on the cable with very much more of the article below the cable than above it. An unsatisfactory solution to this problem is to adhere the highly-expanded substantially round tube 20 to the cable 22 by means of adhesive tape 24, as illustrated schematically by way of example in Figure 2. While this arrangement may reduce the aforementioned displacement on recovery, the taping operation is an awkward additional step which undesirably shows down the whole harnessing process, and the arrangement is still asymmetrical which can lead to distortion or wrinkling on recovery. The relatively flat shape according to the invention is therefore much more desirable, especially for automotive harnessing where high throughput speeds are essential. Although the foregoing advantages could apply to smooth, non- convoluted feed-throughs or other articles such as the well-known "boots" and "udders" frequently used in cable harnessing, it is preferred for the highly-expanded article of this invention to have a convoluted intermediate portion to provide flexibility, especially when the article is made of thermoplastics material which is inherently much stiffer than the rubber used in the previously known feed- throughs. However, it is not a simple matter to produce high-expansion convoluted articles, owing to a tendency for the heat-recoverable plastics material to split at the "corners" of the convolutions, especially at the inner "corners" forming the valleys between successive crests of the convolutions (as viewed from outside the article). For this reason, previously known convoluted heat- recoverable harnessing articles tend to be restricted to expansion ratios less than 2.5: 1, more often less than 2.2: 1 or less than 2.0: 1, whereas expansion ratios greater than 2.5: 1 are preferred for the convolutions in the high expansion articles of the present invention. The resultant threat of splitting on expansion is lessened, according to another aspect of the present invention, by providing at least the inner "corners" (preferably also the outer "comers") of the unexpanded convolutions with a pre-selected radius of curvature (r) of their convex surface which is at least 25% (preferably at least 50%, more preferably at least 75%, and especially 100% or more than 100%) of the average radial thickness (t) of the heat-recoverable material at the "comers" as shown schematically in Figure 3. Pre-selected radii of curvature as much as, or more than, 150% or 200% of the thickness may be desirable in some cases, depending to some extent or trial and error in relation to the characteristics of the material used. As shown schematically in Figure 4, the "corners" will tend to appear as marks or shallow grooves on the surface of the highly- expanded article without detracting from its preferred substantially straight tubular form of substantially constant tubular cross section. Similarly, the lip-and-groove grommet will tend to remain as a minor projection and indentation in the substantially straight tubular expanded article. Preferably, for automotive harnessing, the flat-shaped article has dimensions of about 14 to 15 cm "long axis" (L) to about 2.5 cm "short axis" (S) as illustrated in Figures 1 and 4. Instead of, or preferably in addition to, the controlled radii of curvature of the "corners" of the convolutions, splitting may be resisted by use of reinforcing fillers, which are not normally used in heat-recoverable materials. This aspect of the invention accordingly provides a split-resistant highly-expanded heat-recoverable article comprising thermoplastic polymeric material and a split-resisting amount of reinforcing filler material. Preferably the weight of reinforcing filler used is at least 30%, preferably at least 40%, more preferably at least 50%, of the weight of the polymeric material, suitable reinforcing fillers including, for example a mixture of active silica and low-structure carbon black, preferably in approximately equal proportions. Reinforcing fillers are normally used not in thermoplastics, but in rubbers, as described in pages 279-291 of the "Rubber Technology Handbook" of Werner Hofmann, published by Hanser. The use of reinforcing fillers also seredipitously helps to solve another problem which tends to arise with highly-expanded heat- expanded heat-recoverable articles: the problem known as "amnesia", when the article stops recovering before it has reverted fully to its unexpanded dimensions. Amnesia arises from the reduction of splitting at high expansion ratios by the common practice of reducing the level of cross-linking in the heat-recoverable polymeric material, for example by reducing the electron beam radiation dose or the amount of cross-linking chemical aids in used in known methods of cross-linking. This reduces the heat-recovery ability of the material, resulting in amnesia, but a certain amount of amnesia can be tolerated since most articles are intended to be shrunk down to grip onto an object which is larger than the unexanded diameter of the heat-recoverable article. Thus, the article will grip a plug or connector backshell onto which it is being shrunk before it has exhausted its recovery ability, that is before its amnesia begins to take effect, assuming the size of the article is selected to suit the size of the object taking account of the limitations imposed by the amnesia. Those limitations may, however, be a nuisance, and can be unacceptable, especially when the article is required to return to its unexpanded dimensions in order to fit into an aperature, as is the grommet end of the bulkhead feed-throughs provided by one aspect of this invention. Substantially zero or acceptably low (less than 5%, preferably less than 2%) amnesia can be achieved by increasing the amount of cross-linking, but this is normally at the expense of increased splitting. This aspect of the present invention accordingly provides a highly-expanded heat-recoverable article, preferably a cable harnessing article, comprising polymeric material which is sufficiently cross-linked to provide substantially complete substantially amnesia- free recov to its unexpanded dimensions and comprising a split- resisting amount of reinforcing filler material. Suitable amounts of cross-linking and of reinforcing filler to achieve the desired balance between amnesia-free recovery and split resistance can be determined by trial and error using known compounding methods and test procedures. Preferably, the article according to this aspect of the invention has a snap-fit grommet at one end, preferably a grommet as hereinbefore described. While each of the aforementioned aspects of the invention may be considered alone, or in any permutation or combination with any of the other aforementioned aspects, an especially preferred embodiment of the invention provides a heat-recoverable bulkhead feed-through for cable harnessing having a snap-fit bulkhead grommet means at or near one of its ends, a cable-gripping portion at or near its other end, and a convoluted portion between the grommet means and the cable -gripping portion, which article is highly expanded as aforesaid, preferably in a relatively flat tubular shape, the convolutions preferably having the aforementioned pre-selected radii of curvature, and the heat-recoverable material of the feed- through preferably being crosslinked to a substantially amnesia- preventing degree and preferably incorporating substantially split- preventing amounts of reinforcing fillers. Figure 5 shows schematically such a feed-through 30 having the grommet means 32 snap-fitted into an aperture in an automotive bulkhead 34, with convoluted portion 36 between the grommet means 32 and the cable-gripping portion 36 which has been heat-recovered onto cable 38 passing through the feed-through to the plugs and other devices 39. Slots 33 are illustrated in the skirt of the grommet means to facilitate flexing of the skirt during snap-fitting of the grommet means into the bulkhead aperture. Figure 6 shows schematically a longitudinal section through the feed-through with a preferred shape of groove and lip for the grommet shown magnified in the inset. Suitable polymeric materials for making heat-recoverable articles are well known, having been described in many patent specifications, for example US-A-2027962, US-A-3086242 and US-A- 3597372. In addition to the preferred reinforcing fillers mentioned hereinbefore, the polymers may be compounded by methods known per se with known additives, such as pigments, antioxidants, cross - linking aids, and processing aids. Methods of forming heat-recoverable articles are also well known from the aforementioned patents, among many others. One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heat-unstable, application of heat will cause the article to assume its original heat-stable shape. By way of example, a suitable formulation of material for making a heat-recoverable highly-expanded article according to the present invention comprises, in parts by weight EVA copolymers 100 ("Elvax"-360-LG:75 "Elvax-460R :25) Silica ("Mistron Vapour-RP6) 26.2 Low Structure Carbon Black 25.0 ("Thermax-Flo"-N990-Scalped) High Structure Carbon Black 4.0 ("Statex" N220-Sevalco) Antioxidants (589-36 & 589-24) 2.41 Cross-linking aid ("Ancomer ATM27) 0.81 To this may be added peroxide cross-linking agents and stearate processing aids as known per se. The reinforcing fillers, especially the low-structure carbon black, improve the tear strength and tensile strength of the material. This manner of increasing split resistance is not normally found in heat-recoverable thermoplastics, which normally use large amounts of other, non-reinforcing fillers and merely lower the amount of cross-linking to achieve split resistance at the expense of increasing amnesia, as explained hereinbefore. The above formulation is injection moulded and cross-linked to form a feed-through article similar to that illustrated in Figures 5 and 6, by methods known per se. The feed-through is then heated, expanded on a two -pin expander of pin radius e to suit the gap desired for the short axis S schematically indicated in Figure 1), and cooled to retain the highly-expanded heat-recoverable flat form similar to that illustrated in Figures 1 and 4, with an expansion ratio of approximately 6: 1 at its cable gripping portion, approximately 2.7: 1 at the inner "corners" of its convolutions, and approximately 2: 1 at its grommet ring formation. An automotive cable having plugs and connectors already attached to the ends of its wires is then threaded through the expanded feed-through, which is slid along the cable to the position where it will be required to fit into a bulkhead aperture during car assembly. The flat form of the highly expanded feed-through enables it to grip the cable so as to maintain its position thereon before and during heat recovery in an apparatus shown schematically in Figure 7. The expanded feed-through 40 on cable 42 presents a symmetrical aspect to heaters 44 above and below (not shown) a chain conveyor 46 fitted with supports 48 for carrying the harness between the heaters. Conveyor belts 50 support the respective ends 49 of the harness with the attached plugs and connectors while the feed-through is passing between the heaters. At the end of the recovery process, which preferably takes only 10-15 seconds, the narrower end of the feed- through grips the cable, and its corrugated portion and grommet portions are fully recovered around (but not gripping) the cable, as illustrated by feed-through 40'. The finished, cooling harness is carried off on take-off conveyor 52, and subsequently assembled into a car. That assembly process is facilitated by the harness feed- through having been shrunk onto the cable as aforesaid, in the right position, and with its grommet formation of the right dimensions, for snap fitting into the bulkhead. The heaters 44 may have staggered heat elements arranged to shrink part of the feed-through, e.g. the cable-gripping end, before the other parts. It will be understood that the features hereinbefore described for bulkhead feed-throughs may be used individually or in any combination with other relevant forms of heat-recoverable "boot", sleeve or article, but notably cable-harnessing "boots", sleeves or other articles.

Claims: CLAIMS: 1. A highly-expanded hollow heat-recoverable cable harness article having a relatively flat tubular shape enabling it in use, prior to heat recovery, to grip resiliency the cable onto which it is to be recovered. 2. An article according to claim 1 , which is a cable bulkhead feed- through, preferably having a substantially straight tubular form of substantially constant tubular cross-section. 3. An article according to claim 1 or 2, which is at least partly convoluted in its recovered state. 4. An article according to claim 3, wherein at least the inner corners of the expanded convolutions have an expansion ratio of at least 2.5: 1. 5. A hollow, at least partly convoluted, heat-recoverable article, wherein at least the inner corners of the convolutions have an expansion ratio of at least 2.5: 1. 6. An article according to claim 3, 4 or 5, wherein the convex surfaces of the corners of the convolutions have radii of curvature which are equal to at least 25%, preferably at least 50%, more preferably at least 75%, or especially at least 100%, of the average radial thickness of the heat-recoverable material at the comers. 7. An article according to any preceding claim, incorporating polymeric material and reinforcing filler material, preferably active silicia and/or low-structure carbon black, the weight of the reinforcing filler material preferably being at least 30%, more preferably at least 40%, or especially at least 50%, of the weight of the polymeric material. 8. A highly-expanded heat-recoverable article comprising thermoplastic polymeric material and reinforcing filler material, preferably active silica and/or low-structure carbon black, the weight of the reinforcing filler material preferably being at least 30%, more preferably at least 40%, or especially at least 50% of the weight of the polymeric material. 9. A highly expanded article according to any preceding claim, having less than 5% (preferably less than 2% or substantially zero) amnesia by virtue of being sufficiently cross-linked so to limit the amnesia, and incorporating reinforcing fillers in amounts to prevent splitting at the expansion ratios in question. 10. A highly-expanded heat-recoverable article having less than 5% (preferably less than 2% or substantially zero) amnesia by virtue of being sufficiently cross-linked so to limit the amnesia, and incorporating reinforcing fillers in amounts to prevent splitting at the expansion ratios in question. 11. A heat-recoverable bulkhead feed-through article for cable harnessing having snap-fit bulkhead grommet means at or near one of its ends, a cable-gripping portion at or near its other end, and a convoluted portion between the grommet means and the cable- gripping portion, which article is highly expanded, preferably in a relatively flat tubular shape. 12. A feed-through article according to claim 11 , wherein the convex surfaces of the corners of the convolutions have radii of curvature which are equal to at least 25%, preferably at least 50%, more preferably at least 75%, or especially at least 100%, of the average radial thickness of the heat-recoverable material at the comers. 13. A feed-through article according to claim 11 or 12, having less than 5% (preferably less than 2% or substantially zero) amnesia by virtue of being sufficiently cross-linked so to limit the amnesia, and incorporating reinforcing fillers in amounts to prevent splitting at the expansion ratios in question. 14. An article according to any preceding claim, having a relatively flat tubular shape of aspect ratio at least 4: 1, preferably at least 5: 1, more preferably at least 6: 1. 15. An article according to any preceding claim having a relatively flat tubular shape of aspect ratio less than 25: 1, preferably less than 15:1, more preferably less than 10:1. 16. A highly-expanded article according to any preceding claim at least part of which has an expansion ratio of at least 4: 1 , preferably at least 5: 1, more preferably at least 6:1. 17. An article according to claim 16, all parts of which have an expansion ratio of at least 1.5: 1, preferably at least 1.8: 1 , more preferably at least 2.0: 1. 18. A cable harnessing process wherein an article according to any preceding claim is threaded onto a cable, preferably after connection of the cable wires to plugs and or connectors, and is subsequently heat-recovered to cause part of the article to grip the cable.

Inventors: CROFTS DAVID, FITCH ANTHONY RONALD LESLIE, SHERWOOD ROY PHILIP, CROFTS, DAVID, FITCH, ANTHONY, RONALD, LESLIE, SHERWOOD, ROY, PHILIP
Applicants: CROFTS DAVID, FITCH ANTHONY RONALD LESLIE, RAYCHEM LTD, SHERWOOD ROY PHILIP, CROFTS, DAVID, FITCH, ANTHONY, RONALD, LESLIE, RAYCHEM LIMITED, SHERWOOD, ROY, PHILIP
Application year: 1994
Main classification: B29C61
IPC codes: B29C61, B29K105, B29L23, B60R16, H02G3, H02G15